Prepare and bake Tartlet Shells.
Peel and devein shrimp. Bring water to a boil; add shrimp. Cook 3 to 5 minutes or until shrimp turn pink; drain. Coarsely chop shrimp, and pat dry with a paper towel.
Stir together mayonnaise and next 4 ingredients in a large bowl. Add shrimp, celery, and 2 tablespoons green onions.
Fill each Tartlet Shell with 1 heaping tablespoonful shrimp salad. Garnish, if desired. Serve immediately.
Make Ahead: Tartlet shells can be baked up to 24 hours ahead. Store in an airtight container.